The present invention relates to hydrodynamic resistance of marine vessels such as surface ships and underwater ships, more particularly to methods and devices for conducting model testing of such vessels to predict such resistance.
Ship models are used to carry out hydrodynamic testing in tanks or basins. The model test data may be used, for instance, to design a new full-scale ship or to refine a design of an existing full-scale ship. The famous 19th century engineer William Froude studied hull shapes and formulated the concept of the Froude number, which has since represented a standard for predicting performance of full-scale hulls based on results of model-scale testing.
A typical towing tank is equipped with a towing carriage running on two rails. Depending on the facility and the application, the towing carriage may tow a model or may follow a self-propelled model. A computer collects data and controls speed and/or other variables of the model. Model testing is commonly conducted in relation to resistance or propulsion, for instance to evaluate maneuverability, or powering requirements to attain certain speeds. A towing tank may also be equipped with a wave generator for simulating waves at sea.
Ship resistance greatly impacts design of propulsors and power plants as well as estimation of fuel costs. Due to complex flow around a ship, resistance prediction still relies on model tests and scaling formulae to relate model data to full scale performance prediction. Existing test methods for predicting ship resistance are based on use of “turbulence stimulators” to trigger turbulent boundary layers in ship models. In the marine industry, the technical issues associated with these conventional methods have been well discussed, and the accuracy of resistance predicted thereby is a source of significant concern.
A submerged craft such as a submarine typically includes a bare hull of an axisymmetric body, appendages such as rudders for maneuvering and control, and unique features specifically designed for each class of craft to operate (for instance, a layer of non-skid coating on a hull surface to prevent skid). Due to complex flow around a submerged craft, resistance prediction still relies heavily on model tests and scaling formulas to relate model data to full-scale performance prediction.